Occasionally, curious customers ask us, “Are there materials that can be used to block a magnet?” The short answer: Yes and no. While there’s little you can do to stop a magnet from being a magnet (besides turning up the heat or dropping down to extreme cold), there are a few ways you can contain its magnetic field. 

Blocking a Magnet

As we said, a magnet is constantly trying to attract objects within its magnetic field. In fact, magnets are often able to do this through other objects. It’s the same reason you can clean a fish tank with two magnets and a sponge. But there are three effective diamagnetic materials that will seemingly repel magnetic fields away from themselves, almost like reverse magnets. They are:
  1. Bismuth
  2. Pyrolytic Graphite (the molecular layers of carbon is optimally suited to repelling)
  3. Mumetal (a branded combination of nickel, iron, and other elements)
  While expensive, these materials are excellent tools for protecting items like magnet-sensitive hard drives and medical devices. To be fair, there are other materials that will block magnetic fields, as well. Elements like mercury, tin, and lead can act as superconductors that are very diamagnetic to repel other magnets, but only when they’re at temperatures of -270°C or lower. This makes them expensive and impractical substitutes for bismuth, pyrolytic graphite, or Mumetal.

Absorbing a Magnetic Field

The problem with the three materials listed above: They’re often hard to fit into the company budget. In addition, it’s not always necessary to completely repel a magnetic field. Instead, what’s really needed is absorption. The advantage of absorbing a magnetic field is that it won’t bounce around in another direction. What’s generally required is a ferromagnetic material containing iron, nickel, or cobalt. The thicker this material is, the better it will perform at absorbing a magnetic field. For example: An iron box with solid, one-inch-thick sides would be more than enough to absorb the magnetic flux of a ⅜ inch neodymium magnet placed inside of it, assuming the box was closed and sealed tight. Instead of the magnetic field shooting through the box (like it could shoot through your fish tank in our previous example), it would shoot into the box, where the iron would absorb it and disperse it through itself. This absorption is extremely important during transportation. This is partially because of fragile flight technology, but also because of the need to keep multiple magnets from attracting each other while sitting in such close proximity. So, how are dozens of magnets shipped at once? Ferrous metal sheeting (often made of steel) is placed between magnets to keep them apart. As you would expect, the thicker the magnet, the thicker the sheeting needs to be. In addition, the magnetics are usually stored north-to-south so that they’re less likely to bounce around from attracting each other. Speaking of shipping, we can deliver magnets right to your door. Browse through our catalog to find the perfect magnet to fit your needs, then look through our frequently asked questions for even more help. Want to check the strength of a magnet? Try our gaussmeter.